Large eddy simulation of particle transport and deposition over multiple 2D square obstacles in a turbulent boundary layer

Abstract

Predicting solid particle transport in the lowest parts of the atmosphere is a major issue for man-made obstacles in semi-arid regions. Here, we investigate the effects on solid particle saltation, of square obstacles on the ground with different spacings. The aerodynamic field is determined by large eddy simulations coupled with an immersed boundary method for the obstacles. Solid particles are tracked by a Lagrangian approach. Takeoff and rebound models are introduced for the interaction of particles with the wall. Without particles, fluid velocity profiles are first compared with experiments (Simoens et al., 2007) showing good agreement. Special focus is put on the recirculation zone that plays an important role in solid particle entrapment.Particle concentration fields are presented. Accumulation zones are studied regarding the different obstacle spacings as an extension of the aerodynamic scheme by Oke (1988) to solid particle transport. A deposition peak appears before the first obstacle. When the spacing between the two obstacles is large enough, some particles are trapped within the recirculation and a second deposition peak arises. The streamwise evolution of the horizontal saltation flux shows that the lowest flux downstream of the obstacles is obtained for the highest separation. The deposition rate or the streamwise saltation flux are estimated globally as a function of obstacle spacing. These results illustrate how the numerical tool developed here can be used for assessing air quality in terms of solid particle concentration.

Turbulent Coherent Flow Structures to Predict the Behavior of Particles With Low to Intermediate Stokes Number Between Submerged Obstacles in Streams

“…Despite the wide application and numerous studies on particle transport, the knowledge about their interactions with aquatic ecosystems is still lacking due to the difficulties of analyzing continuous flow and discrete particles simultaneously. Immersed obstacles such as vegetation, bedforms, and hydraulic structures, complicate the analysis by introducing specific ranges of flow structures which affect transport of particles (Chung et al., 2021; Le Ribault et al., 2021; Soleimani & Ketabdari, 2020). Laboratory and numerical studies often simplify the complicated geometry and arrangement of such obstructions to understand how submerged obstacles disturb the flow, and questions remain on how to thoroughly account for the effects of transport mechanism of particles (Follett et al., 2021; Park & Hwang, 2019).…”

“…The evolution of flow structures over multiple obstacles is alike those for a single obstacle, until the spacing between obstacles becomes important and affects the interobstacle flow, similar to the aspect ratio in cavity flow (Schofield & Logan, 1990). Experiments with particles with different geometries of multiple obstacles show varying deposition of particles in response to evolving flow structures in the vicinity of obstacles (Follett & Nepf, 2018; Le Ribault et al., 2021).…”